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Abstract: This paper presents a compact microstrip directional coupler (MDC) based on coupled lines; the multilayer topology of this coupler is optimized for operation in the L-band frequency range. A peculiarity of the proposed MDC design implies that the upper metallization of the multilayer package of printed circuit board (PCB) is used for signal conductors, while the interlayer transitions of the PCB are implemented in metallization of screen for increasing the working thickness of substrate in the region of location of coupled lines. The original synthesis technique for microstrip device topology that takes into account the impact of losses in metal on the characteristics and minimizes the required quantity of the intermediate test boards in practice. PubDate: 2022-07-01
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Abstract: It is considered the procedures of estimation of meteorological formations parameters by the systems of inter period processing of the signals of pulse Doppler weather radars on a background of clutter generated by reflections of the probing signal from ground and sea (water) surface and objects at the earth surface. They are based on estimations of absolute value and phase of auto-correlation spectral density (ASD) of the mixture of the reflections from meteorological formations and clutter. It is shown that procedures using such estimations and Fourier transformation can be implemented with adaptive lattice filters that increases the efficiency of meteorological formations parameters estimation. It is proposed and researched the alternative estimation procedure which is also based on estimation of ASD absolute value and phase but using “high-resolution” Capon algorithm. On a basis of analysis of errors of estimation of meteorological formations reflections spectral moments using learning samples of finite volume it is shown the advantages and drawbacks of proposed estimation procedures. It is shown that among considered procedures it is advisable to use proposed procedure with estimation of the spectral density of input mixture with “super-resolving” Capon algorithms. Generally it satisfies the requirements to estimation errors for different values of parameters of interferences and meteorological formations, especially in dangerous conditions of strong turbulence of meteorological formations. The alternative method to the researched procedures can be the combination of these procedures. PubDate: 2022-07-01
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Abstract: The article shows the possibility of reducing the temperature coefficient for the bandgap voltage reference (BVR) built on bipolar transistors. To do this, as the first step, it is proposed to divide the temperature range of BVR operation into two intervals. Since the most probable working interval corresponds to the range of positive temperatures, such division makes it possible to halve the temperature coefficient for the most probable working area on condition of an appropriate BVR adjustment. The introduction of weights for BVR optimization involves giving preference to the working interval of positive temperatures. It provides a direction of search for the optimal solution when formalizing the optimization process. The second step involves the proposal of a functional block diagram with compensators of the decline of temperature characteristic. The paper also proposes electric circuits of a typical compensator and the circuits for connecting one and two compensators to uncompensated BVR. This also determines the rule of introducing further compensators, if expedient. The parametric optimization of the proposed BVR circuits and the experimental study of BVR circuit with one compensation link have been performed. The above optimization resulted in a reduced value of temperature coefficient at the level of 2.88 ppm/°C for the circuit with one compensator and 1.0 ppm/°C for the case of connecting two compensators to BVR circuit that surpasses the latest published achievements. When expanding the temperature range into the area of low temperatures and using additional compensators in accordance with the specified schematic block diagram, we could expect the reduction of the temperature coefficient to 0.25–0.5 ppm/°C. PubDate: 2022-07-01
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Abstract: The rapid development of various applications and services that use the user’s current LBS location and crowdsourcing require constant improvement of positioning methods in order to improve location accuracy. The problems of local positioning of users indoors in conditions of high concentration of users and the presence of difficulties in the propagation of radio signals deserve special attention. Comparative analysis of known IPS local positioning methods proves the advantage of using the fingerprinting method according to the criterion of positioning accuracy. It is proposed a method of user positioning in a Wi-Fi/Indoor network, which is based on the fingerprinting method and complex spline approximation. We carry out a comparison of the results of positioning in the Wi-Fi/Indoor network based on the fingerprinting method using different methods of user location determination, such as the k-nearest neighbors k-NN method, the weighted k-nearest neighbors k-WNN method and the complex spline approximation based on the quadratic planar spline. It is shown that application of complex spline approximation provides an increase in the accuracy of user positioning in the Wi-Fi/Indoor network, thereby making it possible to provide LBS-oriented services to users indoors. PubDate: 2022-07-01
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Abstract: The key areas of application of systems with microelectrode arrays (MEA) are studying the mechanisms of diseases and testing the effect of drugs on the human body using “laboratory-on-a-chip” technologies based on researches of artificially grown cells. Many scientists’ efforts are directed to the processing and analysis of information received by MEA systems, helping the doctors in creating effective treatment strategies. However, field potentials (FP) of cardiac cells recorded with MEA systems in non-invasive measurements provide incomplete information for the estimation of ionic currents, compared to invasive measurements of action potentials (AP) obtained using patch-clamp technology. The research is devoted to the mathematical determination of the relationship between the signals of electrical activity of cardiomyocytes: internal AP and external FP. In this paper it is proposed a method for solving the inverse problem of the relationship between AP and FP. The equation for the transfer functions between AP and FP is obtained on the basis of field theory. The paper presents the results of AP reconstruction modeling using measured FPs, demonstrating the change in the morphology and parameters of these signals under the influence of dimethylsulfoxide (DMSO). FP signals are recorded using non-destructive electrophysiological technology based on microelectrode coaxial guides (μECG), which can be considered as a type of MEA. PubDate: 2022-07-01
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Abstract: A new kind of modulation has been developed representing Hartley’s amplitude modulation (HAM) that differs from the amplitude modulation (AM) by the presence of two orthogonal components of amplitude-modulated signal making it possible to increase the HAM efficiency to 90% as compared to 33% for conventional AM at the maximum value of modulation index M = 1. The sum of signals of cosine and sine components is used as a signal of the carrier frequency that corresponds to function cas(a) = cos(a) + sin(a), which is applied as a kernel of the Hartley transform. Based on HAM, Hartley’s double band amplitude modulation, i.e., Hartley’s balanced modulation (HBM), and amplitude Hartley’s single sideband modulation (HSSB) were developed. It has been shown that HAM, HBM and HSSB modulations provide for the energy gain of 6 dB making it possible to double the range of communication as compared with the use of AM, balanced modulation (BM) and single sideband (SSB) modulation with the other conditions of signal transmission and reception being equal. While maintaining the specified range of communication at the fixed level, the transmitter power in case of using HAM, HBM and HSSB modulations can be reduced by a factor of 4 as compared with the case of AM, BM and SSB modulations, respectively. The application of HAM and HSSB modulations makes it possible to transmit narrow-band signals at considerable distances using the long, medium and short waves through ionospheric channels of communication with high efficiency, where the use of broad-band signals is difficult. PubDate: 2022-06-01
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Abstract: The paper presents the fault recognition and reconfiguration technique for three-phase five-level cascaded H-bridge multilevel inverter operation. The multilevel inverter operation is carried out by using space vector modulation technique. Open switch fault is very frequent in multilevel inverter, which is located using fuzzy logic whereas the fault reconfiguration is done by adding one auxiliary inverter module with the main multilevel inverter which operates in a faulty condition and regulates the output voltage. The operation of auxiliary inverter module is according to the switching state provided which is based on a fault that occurs in a particular switch. In this method continuous operation of the main multilevel inverter is possible even in the fault condition with only one or two voltage level missed at the output. The continuous operation of multilevel inverter with reduced THD is achieved without using filter which is affirmed by MATLAB® simulation. PubDate: 2022-06-01
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Abstract: The paper considers the schematic diagram and operation algorithm of acoustooptic processor (AOP), the main assemblies of which are acoustooptic modulator (AOM), laser and photodetector (PD). Using the mathematical simulation, it has been shown that the signal at the AOP output contains information about the characteristics of AOM, laser and PD. The possibility of investigating the characteristics of one of the above assemblies with the known parameters of the other two by using the AOP response on determinate input action in the form of rectangular pulse has been established. A brief review of the known methods for measuring the parameters of PD and laser is presented including certain limitations of their applications. The theoretical substantiation of the possible use of AOP peculiarities for measuring the PD inertia parameters is presented. A formula for the calculation of the AOP output response to rectangular input action is proposed that makes it possible to estimate separately the time of optical beam crossing by the elastic wave packet and PD inertia. In addition, it has been proved that the configuration of cross-section of laser beam and the distribution law of power flux density in this beam could be determined on the basis of AOP peculiarities. To this end, a pulse of short duration is fed to the AOP input. Results of theoretical investigations were validated by numerical calculations and confirmed by experimental measurements. PubDate: 2022-06-01
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Abstract: A new type of transmission line representing a semicoaxial waveguide with elliptical cross-section has been proposed. A prototype of such waveguide using the 3D printing technology was created. The transmission coefficient of semicoaxial waveguide with vertical section was measured revealing a quantitative agreement of experimental results with the proposed theory. The possible expansion of working range by 0–30% has been demonstrated in a semicoaxial elliptical waveguide with vertical section that is of practical value. Analytical expressions for wave impedance, transmitted power, losses per unit length of semicoaxial waveguide with elliptical cross-section during the propagation of T-waves therein were obtained. It has been shown that analytically defined losses in metal walls of semicoaxial waveguide agree with the results of simulating its electrodynamic characteristics while using the finite element method (FEM). It was shown that the semicoaxial waveguide with elliptical cross-section and vertical section with air filling could be used in the working frequency range up to 150 GHz in the case of the waveguide planar version. PubDate: 2022-06-01
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Abstract: Over the last decade, mostly in the urban areas, there is tremendous growth in the cellular traffic. The major concerns for cellular network operators nowadays is to deal with ever changing heterogeneity of users and high specification devices. Amidst upcoming technologies, this work illustrates the cellular networks based on massive MIMO (Multiple Input Multiple Output) and on small cells (SC) with both large and small-scale fading environment for signal propagation. The massive MIMO set up network is analyzed with N antennas at the centered macro BS (Base Station) offering services to U users at an instant in the MC (Macro Cell) with sub-6 GHz spectrums. The massive MIMO network is demonstrated with 8×8, 16×16, 25×25, 50×50, and 100×100 configurations. The SCs based cellular network is analyzed with 1 MC and 8 SCs increasing the number of serving users from 50 to 100. The set up network is analyzed with allocation of sub 6 GHz at the MC and mm-wave spectrum at the deployed SCs. The key performance metrics of the set up networks such as sum rate, average user throughput, and energy efficiency are evaluated. With massive MIMO set ups, the plotted result depicts boost in the network sum rate and energy-efficiency with increase in the number of antennas at the centered deployed BS and users in the cell. The SCs based set up also depicts boost in the network sum rate and energy-efficiency with increase in the number of users in the MC with 8 SCs. PubDate: 2022-06-01
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Abstract: This study presents the assessment of the clinical significance of the quantitative criterion of intrahemispheric symmetry (IHS) of cerebral perfusion according to the data of single-photon emission computed tomography (SPECT) with perfusion radiopharmaceutical in patients with mild cerebral injury due to combat trauma. The results of examination of 44 patients were analyzed. The main materials for comparison included SPECT images of brain with 99mTc-HMPAO and data of the neuropsychological testing (NPT), such as assessment of vegetative disorders according to Wayne, the assessment of psychoemotional sphere, the assessment of the symptom severity of traumatic brain injury based on the Cicerone questionnaire, and the assessment of the severity of post trauma stress disorder (PTSD) based on the PCL-military tests. The results of the analysis of scatterograms in brain segments for various quantitative NPT criteria and the IHS criterion showed the data clustering and nonlinear relationship. In some cases, this relationship is characterized by threshold effects (catastrophes and bifurcations). Hence, the assessment of psychoemotional and cognitive impairments based on SPECT and IHS data could be expediently carried out on the basis of piecewise polynomial, linear or parabolic functions. For the first time, the clinical informativeness of the IHS criterion for brain perfusion according to SPECT data has been shown that allows us to assess quantitatively the psychoemotional and cognitive impairments in patients with moderate cerebral injury due to combat contusion accompanied by the development of post trauma stress disorder (PTSD). PubDate: 2022-05-01 DOI: 10.3103/S0735272722050028
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Abstract: This paper presents a study of classical circuit of differential oscillator using rigorous methods of nonlinear theory of electrical oscillations. It is proposed a mathematical model of such oscillator based on the Kirchhoff’s laws application. It is implemented by pass to the model of single-circuit LC oscillator, equivalent to a differential one. A method is developed for such transition with development of nonlinear characteristic of the amplifying element of the equivalent based on nonlinear characteristics of the amplifying elements of a differential oscillator. The mathematical model of the equivalent oscillator is simple and accurate. In case of small values of a small parameter, the traditional method can be used for its analysis, for example, the method of slowly varying amplitudes. For insufficiently small values of a small parameter, expressions are obtained to describe the changes in the amplitude and frequency in oscillations establishing process. The results presented can be useful in the development of various devices based on a differential self-excited oscillator. PubDate: 2022-05-01 DOI: 10.3103/S0735272722050041
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Abstract: The problem of object perimeter protection by human steps detection using autonomous seismic activity sensors is solved in this paper. The results of the CME (consecutive mean excision) and FCME (forward consecutive mean excision) algorithms to calculate these sensors threshold level are presented. The algorithms are tested on real experimental data. The number of false alarms for CME and FCME algorithms is equal to 23% 10%, respectively, operating with the envelope of seismic signal. The possibilities to reduce the number of false alarms for algorithms are explored. The signal trend neutralization allows us to reduce the probability of false alarms to 16% and 7% for the CME and FCME algorithms, respectively. The signal amplitude normalization in the analysis interval makes it possible to reduce the number of false alarms to a negligible value. The results allow us to choose the algorithm depending on the input data specifics. The CME algorithm with preliminary normalization of the signal amplitude is the most appropriate to solve the problem of human steps detection by autonomous sensor due to less computational complexity. PubDate: 2022-05-01 DOI: 10.3103/S0735272722050053
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Abstract: This paper presents a substantiation of relaxation model of dielectric spectra that is based on Debye’s assumption about the dispersion of dielectric permittivity. According to this assumption the electric polarization of polar complexes is lagging at high frequencies of electric field that results in the reduction of dielectric permittivity, while the dielectric loss coefficient achieves its maximum. The paper considers an elementary model of dielectric relaxation. It has been shown that in processing of data of dielectric dispersion under an assumption of single time of relaxation, the accuracy of measurements should be very high. The relaxation spectrum of permittivity dispersion is found to be low-sensitive to the distribution or to interaction of relaxation oscillators. The existing approaches are described for explaining the blurring of dielectric spectra. They include empirical models of Cole–Cole, Fuoss–Kirkwood, Cole–Davidson, and Havriliak–Negami. The paper presents the analysis of the specified models and provides their advantages and disadvantages. A new model (non-empirical) approach is proposed for describing the extended dielectric relaxation spectra. The new approach is applied for materials with uniform and Gaussian distribution of frequencies of relaxation oscillators. PubDate: 2022-05-01 DOI: 10.3103/S0735272722050016
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Abstract: The radio frequency (RF) 4-channel 0–360° range digitally controlled phase shifter is proposed in this article. It is a part of the 4-channel AMMC (amplitude modulation of many components) modulator and demodulator. They are used to generate and process signals for new highly efficient type of amplitude-phase modulation—AMMC. The AMMC modulator and demodulator are parts of a promising highly efficient data transmission telecommunication system. The ability to change the initial phases independently at each output of the phase shifter in the range of 0–360°, high precision of setting the signal phase difference, stability of signal amplitudes, digital control of the signal initial phases at the outputs, and wide range of operating frequencies using specialized software are the advantages of the proposed phase shifter. The designed phase shifter can be used in the high speed data transmission telecommunication systems to generate or process PSK (phase shift keying), ASK (amplitude shift keying), QAM (quadrature amplitude modulation) and AMMC signals. Also it can be used in the high-reliability telecommunication systems with complex control system and hot redundancy. PubDate: 2022-05-01 DOI: 10.3103/S073527272205003X
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Abstract: In this brief, various multi-operand parallel prefix adders are designed and they are implemented in fused multiply-accumulate (MAC) unit. A multi-operand adder is the fascinating technique in contrast with a network of 2-operand adders in many arithmetic applications. Also, the parallel prefix adder is one of the high speed adders. Thus, multi-operand adders are designed using various parallel prefix graphs which are used for implementing fused MAC unit. Initially, the parallel prefix adders are structured and analyzed. Secondly, the designed parallel prefix adders are restructured for multi-operand operations. Finally, MAC unit is implemented using various multi-operand adders. The proposed multi-operand parallel prefix adders are designed in Xilinx Kintex 7 FPGA. In contrast with existing one, the Ladner Fischer multi-operand adder provides optimum results based on the power consumption, area and delay. In accordance with the results attained from Kintex 7 FPGA, the Ladner Fischer multi-operand adder outperforms based on power consumption by 38.06%, path delay by 17.54% and number of LUTs by 26.55% against the existing one. Subsequently, the Fused MAC unit designed using Ladner Fischer multi-operand adder provides the reduction in power consumption by 39.95%, path delay by 16.83% and number of LUTs by 13.73% in contrast with the classical MAC unit. PubDate: 2022-04-01 DOI: 10.3103/S0735272722040057
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Abstract: This paper addresses the problem of displacement measurement by a three-probe implementation of microwave interferometry in cases where the reflection coefficients of the object under measurement (target) and the antenna are comparable. The paper presents a three-probe displacement measurement method that accounts for the antenna reflection coefficient. In this method, the target displacement is determined from two quadrature signals using a phase unwrapping technique. The expressions for the quadrature signals include the unknown magnitude of the target reflection coefficient. To determine this quantity, an equation that relates it to the detector currents and the antenna reflection coefficient is derived. It is shown that the magnitude of the target reflection coefficient is given by the smaller positive root of this equation provided that the sum of the target and the antenna reflection coefficient magnitudes is no greater than one. Because of the smallness of the antenna reflection coefficient, this condition is almost always met in free-space measurements. To verify the proposed method, determining the displacement of a target executing a sine vibratory motion was simulated. The simulation showed that if the target and the antenna reflection coefficients are comparable, the method offers a several-fold reduction in the displacement determination error in comparison with the case where the antenna reflection coefficient is ignored even in the presence of a marked noise component in the detector currents. The proposed method may be used in the development of microwave displacement sensors. PubDate: 2022-04-01 DOI: 10.3103/S0735272722040021
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Abstract: Three groups of resonance equations for various resonators on transmission lines (TL) with lumped elements are proposed. They are based on a two-port network parameters. Using these equations, it is established that a third of all resonant frequencies in the known dual-mode stub resonators analyzed using even and odd modes, were not previously taken into account. The proposed equations made it possible to design two new dual-mode resonators from TL segments with all short-circuited ends, which are practically useful. It is shown that the widely used method of even-odd modes cannot be used to describe the properties of new resonators. In the same time, these proposed resonance equations describe new properties of some dual-mode resonators. In particular, dual-mode resonators with a quarter-wave stub, in addition to dual-mode oscillations, also have single-mode oscillations. These two types of oscillations alternate with each other. In contrast, only dual-mode oscillations exist in short-stub resonators. Theoretical results are confirmed by EM simulation. PubDate: 2022-04-01 DOI: 10.3103/S0735272722040033
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Abstract: The article is devoted to a comparative analysis of the results of experimental studies of an adaptive MTI system (moving target indication) based on adaptive lattice filter (ALF) and standard non-adaptive MTI systems of working pulse radars of various applications and wave ranges. This analysis is performed using the seminatural experiment method based on digital recordings of real clutter. Adaptive antijamming systems promptly extract the necessary information about the parameters and characteristics of the interference directly from the input signals, track changes in these characteristics and promptly change their parameters (and, if necessary, the structure) based on the results of the corresponding processing of samples of the received interference of finite volume. It has been shown that the adaptive ALF-based MTI system provides significant gains in the effectiveness of radar protection from clutter as compared with non-adaptive standard systems of working radars and the stable tracking of air targets in the area of intense clutter, while target drop-outs are observed at the output of standard non-adaptive MTI systems. PubDate: 2022-04-01 DOI: 10.3103/S073527272204001X
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Abstract: Underground coal mine environmental monitoring is required to ensure and maximize the safe working conditions in mines. For safety monitoring, there is a need to develop an active communication and information network that will be able to detect quickly and efficiently the mine environmental condition and take necessary actions to warn the workers about the environmental condition of the mining area. This can be achieved by the application of long-range wireless communication technology. In the present study, we designed and developed an embedded sensor module to monitor the multiple parameters of environment, including temperature, humidity, methane, carbon monoxide, hydrogen, and coal dust. These multi-parameter monitoring sensors have been interfaced with an Arduino microcontroller. The XBee S8 Ultra-High Frequency (UHF) transceiver device has been used to enable the long-range communication. The specified parameters have been predicted for the safety tenacity in the underground coal mine. A new approach for the calibration process of gas sensors and coal dust sensor has been suggested to acquire desired gas concentrations and dust density in the underground mine air. The computer has been interfaced with the system for environmental multi-parameter monitoring. A successful laboratory trial has been made under the real conditions. In addition, the rangeability of the UHF radio transceiver device and power management of the embedded monitoring module have also been discussed. PubDate: 2022-04-01 DOI: 10.3103/S0735272722040045
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